I'm currently writing optimisations for a raster viewer program which uses gdal
as it's base. It's currently written purely in python, and has some major speed
issues which cause problems when we are reading many files at a time. After
making some optimisations in the python, and getting quite a minimal speed
increase, I proceeded to profile the program quite heavily and found that our
getImage method was our slowest call. I had already performed some
optimisations on this function so decided to write a C-Extension so that we
could get some speed increases through a lower level language.
This has worked for the most part, however there is still one issue, we have
found a speed increase of ~2s for some of our larger files in the bulk of the
code. But this is negated by the GDALRasterIO call, which is actually about 3s
slower than the python ReadAsArray.
This doesn't make any sense to me as ReadAsArray is a wrapper around a C++ call
to GDALRasterIO, and thus should be slower than having a call straight to
GDALRasterIO.
I was hoping someone here might know of a way to read the rasters more
efficiently. I have tried to implement a method using ReadBlock rather than
RasterIO, but due to the replication that RasterIO does it didn't work at all.
(I'm currently trying to figure out a way to do that replication without losing
too much speed).
The RasterIO call i'm using is
band->RasterIO(GF_Read, this->ovleft, this->ovtop, this->ovxsize,
this->ovysize, dataTmp, this->ovxsize, this->ovysize,
band->GetRasterDataType(), 0, 0);
The old python call was:
dataTmp = band.ReadAsArray(ovleft, ovtop,
ovxsize, ovysize,
dspRastXSize, dspRastYSize)
Thanks in advance
Gareth Jones
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